The invention relates to a method for the automatic control of contaminant reduction as applied to gas engines using a sensor in the form of lambda probe adapted to produce a probe potential as an input quantity, the air/fuel ratio lambda being basically able to be set to a value of less than unity and being able to be kept constant as far as possible over the full load range of the engine, a servo member being actuated, more especially at regular intervals until the lambda probe detects an air/fuel ratio of unity and the mixture is enriched again by one of a series of equal steps until the desired air/fuel ratio lambda has been set.
In this method, assumed to be known, of catalytic contaminant reduction in which the air/fuel ratio is able to be set to a value less than unity and as far as possible kept constant over the full load range of the gas engine, a lambda probe is used whose potential is only defined exactly for the stoichiometric point (at which lambda is then equal to 1.0). At all other points, including the operating point of lambda less than unity relevant in the present case, there is no exact correlation between the air/fuel ratio and the probe potential. A conventional automatic control system using the probe voltage as an input quantity would no longer be satisfactory.
This shortcoming may however be overcome by an automatic control system, which is orientated at certain times with respect to the reference point at which lambda is equal to unity, this being done by operating the servo actuator at regular intervals in time until the lambda probe detects an air/fuel ratio of 1. Thereafter the mixture is enriched by a constant adjustment step again to attain the desired air/fuel ratio independently of the instantaneous probe potential during operation. The actuator for varying the air/fuel ratio is then latched in its new setting until the reference point is again to be sought, whereafter the mixture is enriched in equal steps. Such a method has been previously proposed, but it suffers from the disadvantage that during the intervals between seeking the reference point it is not possible to carry out regulation to overcome disturbances affecting the system.